Abstract Language delay is often one of the first concerns of parents of toddlers with autism spectrum disorder (ASD), and early language abilities predict broader outcomes for children on the autism spectrum. Yet, mechanisms underlying language deficits in children with ASD remain unspecified. One prominent component of linguistic behavior is the use of predictions or expectations during learning and processing. Several researchers have recently posited prediction-deficit accounts of ASD. The basic assumption of the prediction accounts is that information is processed by making predictions and testing violations against expectations (prediction errors). Flexible (neurotypical) brains attribute differential weights to prediction errors to determine when new learning is appropriate, while individuals with ASD are thought to assign disproportionate weight to prediction errors. These prediction deficits are hypothesized to lead to higher levels of perceived novelty, resulting in `hyperplasticity' of learning based on the most recent input. The proposed project will be the first study to examine whether language deficits in young children with ASD are linked to atypical domain-general prediction processes. Seven studies are proposed to address the following Specific Aims: (1) to determine the ability of toddlers with ASD to generate predictions compared to typically developing (TD) peers; (2) to establish whether toddlers with ASD exhibit hyperplasticity of learning relative to TD peers; (3) to examine the extent to which certain child characteristics predict individual variability in predictive behavior and hyperplasticity in toddlers with ASD; and (4) establish whether predictive behavior or hyperplasticity of learning on verbal/visual tasks predicts vocabulary and/or syntactic ability one year later in young children with ASD. The sample will be comprised of 75 ASD toddlers (three cohorts of 25 toddlers) and 75 TD controls distribution-matched on cognition (raw scores), SES, and sex. In this project we will utilize anticipatory eye movements (AEMs) and looking-while-listening (LWL) methods to investigate prediction in visual and verbal tasks in toddlers with and without ASD. Studies 1 (auditory) and 2 (visual) examine prediction as indexed by AEMs under conditions in which probabilities of the occurrence of events are relatively stable. Studies 3 (verbal) and 4 (nonverbal) will investigate hyperplasticity of learning in AEM tasks in which probabilities of the events change and predictions must be updated. Study 5 will explore hyperplasticity within the context of novel word learning using a LWL task. Study 6 will examine the relationship between child characteristics (cognition, language, autism symptom severity) and prediction. In Study 7, performance on Studies 1-5 will be used to predict language abilities in the same sample of toddlers one year later (from 18-35 mo to 30-47 mo) using both standardized tasks and an online incremental language processing task. All studies were developed to have minimal task demands in order to include toddlers with ASD across a wide range of functioning. Findings from this research will provide important new insights into ASD phenotypes and mechanisms underlying language development that could open new pathways for intervention.